1. Field of the Invention
The invention relates to a sight, and more particularly to a range finder.
2. Description of the Related Art
U.S. Pat. No. 4,263,719 discloses a sighting device for use as a telescope. The sighting device has a predetermined magnification ratio and a plurality of distance scales marking different distance values for comparing with an image of a subject.
Another laser sighting device is disclosed in US patent application publication No. 20060010762, which uses time difference between emission and reception of a laser beam to calculate distance from a subject. However, the laser sighting device needs to be equipped with a laser diode (LD) and an avalanche photodiode (APD) for emitting and receiving the laser beam, thereby resulting in greater volume and higher cost, and needs electrical power for distance calculation.